1. Field of the Invention
This invention relates to paper supply mechanisms of the type that are used with ink jet printers, facsimile machines, copiers and the like. More particularly it relates to an improvement in a roll feed mechanism in which the paper supply is stored within a drum, travels around the outer surface of the drum, where writing or imaging operations take place, and is then delivered from the drum.
2. Brief Description of the Prior Art
Many different arrangements have been used to handle paper and other sheet materials automatically in connection with drum type imaging devices. In some of these, cut sheets are fed individually from a supply stack, and in other feed systems, paper is fed from a continuous roll into the reproducing equipment and is cut into individual sheets either before or after the imaging operation. In another system, the paper supply is stored within an imaging drum and is withdrawn and wrapped around the drum for the imaging process.
Photocopier machines have used similar mechanisms to supply web in incremental replacement portions to the outside of a photocopier drum and then return the used web to a storage roll within the drum. Examples of such machines are shown in U.S. Pat. Nos. 4,097,138 to Kingsley; 4,102,570 to Shimoda; 4,231,652 to Moser and Wegmann; and 4,239,375 to Eisbein and Wegmann.
It is necessary in an ink jet printer that during the imaging process the sheet material be tensioned tightly around the imaging drum, because there is only a few thousandths of an inch clearance between the drum and the ejection orifice of the print head.
In systems where the used sheet material is returned to the interior of the imaging drum, the tensioning problem is not difficult and may be handled in a number of ways. However, when the sheet material is a processed image to be preserved, the free end remaining after severing the sheet material makes it difficult to tension the material around the drum for the ensuing imaging process.
U.S. Pat. No. 3,829,208 to van Meljel discloses a copy machine in which a supply of sensitized web material is stored on the axis of and within the drum and withdrawn around the outer surface of the drum. The web is utilized during the rotation of the drum to produce photocopies and when it is to be replaced by a fresh supply of web, the fresh web is drawn from within the drum and wrapped around the exterior while the used web is discarded away from the drum. The driving force for the web is provided by two pairs of rollers; a first pair carried by the drum, which engage the web only after it has passed around the exterior drum surface, and a second pair of rollers which are spaced from the drum and mounted in a fixed position relative to the rotation of the drum. Both pairs of rollers apply traction force across the entire width of the web. Tensioning of the web is provided by a roller mounted on an arm within the drum that is spring biased against the web in the space between the supply roll and the exit slot in the drum.
This arrangement provides a tension force that varies with the amount of web material remaining within the drum and limits the maximum capacity of the drum. None of the patents discloses a tension arrangement that is optimal for use with paper medium of the kind that is oridinarily used on ink jet printers. The drive mechanisms described in the above patents, although generally satisfactory for heavier web materials in the particular applications, are not generally suitable for ink jet printers and are likely to cause skewing of paper by the drive mechanism.